Photographic silver halide emulsions stabilized with tetrazaindene compounds



United States Patent 3,2tl2,5l2 PHGTOGRAPEHC SELVER HALIBE EMUL- SEONS STABEHZED WHH TETRAZAIN- RENE $MFUNBS Leslie Alfred Williams, Wealdstone, l rindlesex, England, assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Feb. 23, 1962, Ser. No. 175,233 12 'Qlaians. tfl. %-lil9) This is a continuation-inpart application of my application of my application Serial No. 86,007, filed January 31, 1961, now abandoned.

This invention relates to the synthesis of certain tetrazaindene compounds, as well as photographic products stabilized therewith.

It is well known that certain tetrazaindene compounds can be synthesized by condensing an alkoxymethylenemalonic acid ester with a 3-amino-l,2,4-triazole. However, such condensations have traditionally been carried out under neutral or acidic conditions, and it has been found that it is not possible to produce 6-orio-l,3,3a,7- tetrazaindene compounds by this process.

It is, therefore, an object of my invention to provide a method of preparing 6-oxo-l,3,3a,7-tetrazaindene compounds. A further object is to provide novel 6 oxol,3,3a,7-tetrazaindene compounds. Still another object is to provide photographic emulsions which have been stabilized by treatment with small amounts of such tetrazaindene compounds. Other objects will become apparent from a consideration of the following description and examples.

I have found that the above objects can be accomplished by condensing an alkoxymethylenemalonic acid ester with a 3-amino-l,2,4-triazole compound under alkaline conditions. Many of the tetrazaindene compounds which can be obtained according to my invention can be represented by the following general formula:

wherein R represents a hydrogen atom, an alkyl group, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, etc. (e.g., an alkyl group containing from 1 to 4 carbon atoms), an aryl group of the benzene series, such as phenyl ,o-, mor p-tolyl, etc. (e.g., a monocyclic aryl group of the benzene series, an amino group, such as amino, methylarnino, piperidyl, morpholinyl, etc., an alkylmercapto group, such as rnethylmercapto, ethylmercapto, etc., or a mercapto grou R represents a hydrogen atom, a carboxyl group (including water-soluble salts thereof, such as sodium, potassium, pyridinium, triethanolamrnonium, etc), or a carbolkoxyl group, such as carbomethoxyl, carboethoxyl, carbobutoxyl, etc., and R represents a hydrogen atom or a lower alkyl group, such as methyl, ethyl, etc.

According to my invention, the tetrazaindene compounds of Formula I, wherein R represents a carbalkoxyl group, can be prepared by condensing one molecule of an 3,Z@Z,5l2 Patented Aug. 2 1965 .alkoxymethylenemalonic acid ester of the following general formula:

( mpou=o oooau2 wherein R has the values given above, R and R, each represent a lower alkyl group, such as methyl, ethyl, propyl, butyl, etc., with one molecule of a 3-amino-l,2,4- triazole compound of the following general formula: (III) g ILIT -NHs wherein R has the values give above. As indicated above, the condensation of the compounds of Formula II with those of Formula 111 is carried out under alkaline conditions. By alkaline conditions, I mean under conditions of a pH of at least about 8.0. Of course, more basic conditions than a pH of 8.0 can be employed, and it is to be understood that my invention is not limited to that particular pH condtion. Suitable basic condensing agents include alkali metal alkoxides, such as sodium methoxide, sodium ethoxide, sodium propoxide, sodium butoxide, potassium ethoxide, etc. Alkali metal hydroxides can also be employed as basic condensing agents, typical examples of which include sodium hydroxide, potassium hydroxide, etc. The condensation can be carried out in the presence of an inert diluent, such as a lower alcohol (e.g., methanol, ethanol, propanol, etc), 1,4-dioxane, diethyl ether, etc.

The condensations can be accelerated by heating, although temperatures varying from ambient temperatures (ca. 25 0) to the reflux temperature of the reaction mixture can be employed.

The tetrazaindene compounds of Formula I above, wherein R represents a carboxyl group, can be obtained by de-esterifying the compounds of Formula I, wherein R represents a carbalkoxyl group. De-esterification can be effected by simply heating the esterified derivatives in the presence of a strongly alkaline aqueous solution, such as an aqueous solution of sodium hydroxide, potassium hydroxide, etc. The free acid compounds (R is carboxyl) can be obtained by simply acidifying the deesterification mixture.

The compounds of Formula I, wherein R represents a hydrogen atom, can be obtained by decarboxylation of the compounds of Formula I, wherein R represents a carboxyl group. Decarboxylation can be effected by simply heating the carboxyl derivatives on an oil bath at a temperature of at least about 25 0 C.

As indicated above, the condensation of the compounds of Formula II with those of Formula Ill can be effected under basic conditions to provide the 6-oxo compounds of my invention. A very strongly basic agent, such as sodium ethoxide, will give entirely, or almost entirely, the 6- xo compound of Formula I accompanied by little, or none, of the corresponding isomeric 4-oxo compounds of the prior art. When R of Formula ill is not strongly electron donating, e.g., hydrogen, lower alkyl or mercapto, it is frequently possible to use a rather weak basic condensing agent, such as pyridine, a luitidine, a collidine, etc., in which case there is obtained a large yield of the 6-oxo compound of my invention, or a mixture containing the 6- oxo compound, together with some isomeric 4-oxo compound, from which the 6-0240 compound can be easily separated. When R of Formula III is strongly electron donating, such as amino, a very strong basic condensing agent, such as sodium ethoxide, should be employed.

The following examples will serve to illustrate more fully the manner of preparing 6.-oxo-1,3,3a,7-tetrazindene compounds according to my invention.

Example 1.5-ethoxycarbonyl- -metlzyl-6-0x0- 1 ,3,3a,7-tetrazaindene H :0 0 CH mowed-( g r N, 25.4; C H N O requires C, 48.6; H, 4.5; N, 25.3%.)

Example 2.5-canboxy-4-methyl-6-oxo 1,3,3z'z,7-tetrazaindene /N\ %N 0:0 0 011 i HO 0 04K C 311 g The above ester (26 g.) was refluxed in 10% aqueous caustic soda solution 150 cc.) forl hour. After cooling,

the solution was acidified with concentrated hydrochloric acid and chilled. The product (21 g.) was recrystallized from water as colorless crystals, M.P. 228-229? C. with gas evolution. (Found C, 43.6; H,'3.4; N, 29.7;

w s i s requires C, 43.3; H, 3.1; N, 28.9%.)

Example 3.4-methyl-6-0xQ-1,3,3a,7-tetrazaindene ,The acid obtained in Example 2 (5 g.) was heated un-- der vacuum in an oil-bath at 280 C. The solid'melted' with evolution of gas and the product 'sublirned into a short air condenser. It (3 g.) was recrystallized from water as colorless plates, M.P. 266-267 C. (Found C,

chilled and acidified with concentrated hydrochloric acid to give colorless crystals which were recrystallized from 50% acetic acid as glistening needles, M.P. 214 C. Yield 12 g. (Found C, 44.3; H, 4.6; N, 20.3; S, 11.9; C H N O S requires C, 44.7; H, 4.8; N, 20.8; S, 11.9%.)

Example 5.5 carboxy 4-methyl-Z-methylthio-6-0xo- 1,3,3a,7-tetrazaindene 5 ethoxycarbonyl 4-methyl 2-methylthio-6-ox0- 1,3,3a,7 -tetrazaindene (2.2 g.) was refluxed in 10% aqueous caustic soda solution (20 cc.) for 1 hour, after which the solution was cooled and acidified with concentrated hydrochloric acid. The precipitate (1.5 g.) was collected and Washed with.water and recrystallized from'water as colorless crystals, M.P. 236 C.

Example 6.4 methyl 2-methylthi0-6-0x0-1,3,3a,7-

' tetrazaindene' 5 carboxy 4 -methyl-2-methylthio-6-oxo-l,3,3a,7- tetrazaindene was heated under vacuum to its melting point until the evolution of carbon dioxide ceased. The product was recrystallized from water as colorless needles, M.P. 28'0281 C, (Found C, 42.2; H, 4.3; N, 28.9; S, 16.3; C H N OS; requires C, 42.6; H, 4.6; N, 28.4; S, 16.3%.) i 1 Example 7. 2 amino 5 ethoxycarb0nyl-4-meflryl-6- 2,5 -,diamino 1,2,4-triazo1e (9.9 g.) and diethyl aethoxyethylidenemalonate (23.0 g.) were refluxed together in ethanol co.) in which sodium (2.3 g.) had previously been dissolved. Afiter 33.5 hours, water (60 cc.) was added and the solution acidified. The solid (5 g.) was collected and recrystallized from water as needles, M.P. 300 C. (Found C, 45.2; H, 4.7; N, 29.9;

47.8; H, 4.1; N, 37.5; requires C, 48.0; H, 4.0; N, 37.3 7

Example 4.-5 etlzQxycarbon)l-4-methyl-2-methylthio- 6-0x0-1.,3,3a,7-te'trazaindene Sodium (2.3 g.) was dissolved iri alcohol (60 cc.) and to this solution diethyl r-ethoxyethylidenemalonate' (23.0

. g.) and 3-am-ino5- methylthio-1,2-triazole (13.0 g., Ber. 54B 2089 (1921)) were'added. The mixture was re-- fluxcd for 1.5 hoursby which time the whole headset to a solid. Water (60 cc.) was added and the solution a Example: 8.2 amino 5 carb0xy-4-methyl-6-oxm 7 l,3,3a,7 -tetrazair zdene The ester made asin Example 7 i (4 g.) was refluxed in 10% aqueous caustic soda solution. (40 00.) for 1 hour. A fter cooling,.the product was precipitated by the addition of concentrated hydrochloric'acid, It (2.5 g.)

was purified by dissolving in causticsoda, treating the. solution with. charcoal and re-precipitating with hydrochloricacid. The product was suspended in hoiling water to remove all inorganic impurities, M.P. 360 C. (Found C, 40.0; H, 3.5; N, 33.5; C7H7N5O3; requires C, 4-0.2; H, 3.4; N, 33.5%.)

Example 9.2 amino 4 nzethyl-6-0x0-I,3,3n,7-tetra- Zaindene The above acid (Example 8, 1.5 g.) was heated under vacuum until all had sublimed into a short air condenser. (The starting material did not melt.) The product was collected and recrystallized from water as colorless needles, MP. 357 C. Yield 1 g. (Found C, 43.3; H, 4.4; N, 42.9; C H N O requires C, 43.6; H, 4.2; N, 42.4%.)

Example 10.5 etlzoxycarbonyl-2-methylrhio 6-0x0- 1,3,3a,7-tetrazaindene Sodium (2.3 grams) was dissolved in alcohol (60 ccs.) and to this solution 3-amino-5-methylthio-1,2,4-trizole (13 grams) and dicthyl-ethoxymethylidene malonate(21.6 grams) were added. The mixture was refiuxed for about 16 hours after which water (400 ccs.) was added and boiled to bring into solution. The solution was acidified while still boiling. It was cooled to room temperature and the crystals which formed and contained the 4-ox-o isomer of the required compound, were discarded. The filtrate was chilled to 4 C. whereupon colorless needles of the required 6-oxo compound separated and were filtered. These crystals were recrystallized from water to a yield of 2 grams (MP. 209,210 C.). (Found C, 42.7; H, 4.2; N, 21.8; S, 12.9; C H N O S requires C, 42.7; H, 4.9; N, 22.0; S, 12.6%.)

The following example will serve to illustrate a different preparation for the compound of Example 1 above, using a weak basic condensing agent, such as pyridine.

Example l1.5 etltoxycarbonyl 4 methyl 6 0x0- 1,3,3a,7-tetrazaindene 3-amino-l,2,4-triazole (4.2 grams) and ethyl Z-ethoxyl-ethoxycarbonylcrotonate (11.5 grams) were refluxed together in pyridine cc.) for 16 hours. During this reaction, both the required 6-oxo compound and the isomeric 4-oxo compound are formed. After cooling this mixture, ether (90 cc.) was added, and the mixture was shaken for about 2 minutes. The precipitate, which contains the 4-oxo compound as a pyridinium salt, Was collected and discarded. The desired product was obtained as crystals on further chilling the filtrate. (Found C, 48.5; H, 4.9; N, 25.4; C d-1 N 0 requires C, 48.6; H, 4.5; N, 25.3%.)

I have also found an improved method for making the intermediate starting compounds of Formula II which gives surprisingly higher yields than the known methods of making these compounds, especially in those cases where R represents a lower alkyl group. According to this improved method, an alkyl orthoacetate is condensed with an alkyl malonate, preferably with heating, in the presence of a basic condensing agent, such as an alkali metal allroxide (e.g., sodium ethoxide, potassium ethoidde, sodium propoxide, etc.), an alkali metal hydroxide (e.g., sodium hydroxide, potassium hydroxide, etc.). The following example will serve to illustrate the preparation of such an intermediate.

Example 12.D1'etlzyl- -ethoxyethylidenemalonate Ethyl orthoacetate (324 grams), ethyl malonate (320 grams) and powedered anhydrous potassium hydroxide (5.6 grams) were heated together in an oil-bath. The temperature was raised during /2 to /4 hour to 170 C. by which time the distillation of alcohol commenced, and

was collected after fractionation through a short column. Heating was continued and the temperature raised as necessary to maintain the distillation of the alcohol. After about 4 hours (bath temperature 205 C.) the distillation of alcohol ceased (200 ccs. were collected). The reaction mixture was allowed to cool to C., a vacuum was applied and heating was recommended. A small fore-run (below BP. at 96/2 mm. pressure) was obtained and discarded, while the crude product was collected between 96-130 C. at 2 mm. pressure. This fraction was re-distilled and the fraction boiling (between 96 98 C., 2 mm.) was collected and was purified further by the method described by McElvain and Burkett in the J.A.C.S. vol. 64, page 1831 to give grams of the required compound as crystals, MP. 2527 C. (Found C, 57.5; H, 8.1; C11H1305 requires C, 57.4; H ,'7.8%.)

The 6-oxo compounds of my invention can be added to ordinary photographic silver halide emulsions in order to stabilize such emulsions and prevent the formation of fog upon storage of these emulsions, particularly under adverse conditions, such as high temperatures and humidity.

Fog depends both on the emulsion and the conditions of development; for a given emusion it increases with the degree of development. With constant development conditions, it tends to increase with time, temperature and' relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is, or course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor,, and strongly reducing materials. While antifoggants and stabilizers may protect, to some extent, against such effects, it is normally understood that an antifoggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both.

The 6-oxo compounds of my invention can be used in a variety of photographic silver halide emulsions, in cluding those used in the manufacture of fast negative materials and X-ray elements. The stabilizing compounds of my invention cause an elevation in the emulsion speed when using high intensity exposures, while the low intensity speed is not impaired to the degree associated with other related and isomeric stabilizers. It has aiso been found that many of the 6-oxo compounds of my invention have little or no detectable effect upon the spectral sensitivity of photographic silver halide emulsions containing them, while this is not true for many other tetrazaindene stabilizing compounds.

The following data will serve to illustrate the useful stabilizing or antifoggant effect of many of the compounds represented by Formula I of my invention. These data were obtained using an ordinary high-speed silver bromiodide emulsion (negative type) which had been panchromatically sensitized with a cyanine dye. The sensitized emulsion was divided into several batches, and each batch was separately treated with a quantity of stabilizing compound in the amount shown in the tables. One batch of each emulsion was not treated and this particular batch served as a control. The separate batches of emulsion were then coated on an ordinary support, such as cellulose acetate and dried. Samples of the dried coatings were then immediately exposed on an Eastman lb Sensitorneter with tungsten illumination and developed for 5 minutes in Kodak Developer DK-SO at 68 F. with good agitation. The developed coatings were then fixed, washed and dried in the usual manner.

n the accepted procedures.

7 The relative speeds, gammas and togsof each of the coatingswerethen measured in the usualmanner. V

Separate samples of the above coatings were incubated 1on2; weeks at 120" F. with constant humidity andthe swam water-soluble salts (Lowe and Jones U.S. Patent 2,521,- 926, "issued September 12, 1950). I

' The emulsions may also contain speed increasing compounds of the quaternary ammonium type of Carroll U.S.

incubated strips were then-enposed and processed exactly 5 nt 2,2 issued fip y Carroll and as the fresh coating? I Th? rglgtiye spgeds, h and Allen U.S. Patent 2,288,226, issuedIune 3 0, 1942; and Care fogs for'the various coatings were thenmea m d 1 roll and Spence U.S. Patent 2,334,864, issued November fore. 1 The relative speeds in each instance are inversely 1943; or h Polyethyleng l l type of Canon n proportional tome exposure required to produce a den Beach U.S. Patent 2,708,162, 1ssued May 10, 1955; or veloped density of 0.3 above fog. The DK-SO DeveL the quaternary ammomumrsalts I polyethylen-e'glycols at has the followinb form-111a; 1 I of Piper US. Patent 2,886,437, lssued May 12, 1959; as l? I. I rams well as the thiopolymers of Graham and Sagal U.S. appliv v I 72. cation S er al No. 779,839, filed December 12, 1958, now g gfg g 5 136x101 Sulfate: I I II US. Patent No. 3,046,129 and the Dann and Chechak sodiungsulfite U.S. application serial No. 779,874, filed DecemberdZ, Sodium mtaborate I II """7 '7 1958, now U.S. Patent No. 3,046,134. I PotassiufiiIbromideI f 7 The addenda which I havedescribed may be used in Water to makeIl various kinds of photographic emulsions. In addition to 7, I v being useful in X-ray and other nonopticallysensitized The following data were obtained: I emulsions, they may also be used in orthochromatic,

I I TABLnA' I C t V "Fresh Tests 2Weeks Inc., V. 0a 111 Numbei r. DescriptiOn (gJAg mole) V I I I I 'I I Rel. 'y Fog Rel. 'y Fog. I I Speed Speed I 5-Eiarb0x1y4-methyl-6-0xo-l,3,3a,7-tetrazain- 68 1.42 .08 V I 65 1.15 .14

ene, g; Control- I 100 1.07 .10 71 0.75 .34 4-methy1-6-oxo-1,3,3a,7-tetrazaindene, 3.0 g 85 1. 15 09 105 O. 98 12 5-ethoxycarbonyl-4-n1ethyl-6-oxo-1,3,32.,7- 85 1.12 I .09 100 1.00 11 tetrazeindene, 3.0 g. I

V 1 Week Inn, 120 1:.

con'tmi nu; 100 1.17 .15 s2 1.00 Q33 5-ethoxycarbonyl-4-rnbthyl-2-methylthio45: 102 1.27 .12 100 1.15 .14

oxo-1,3,3a,7-tetrazaindene, .15 g. r I i I fi-carboxy-4-methyl-2-methy1thio-6-ox0-1,3, 95 1.23 .12 97 1.17 .13 I 3a, 7-tetrazaindene, .15 g. I I II I 2-amino-fi ethoxycarbonyl-4-methyl-6-oxo-1, 105 1. 18 .13 I 95. II 1. 08 I .25 I

3,3a,7-tetrazaindene, .75 g. I I. I V I Z-amino-5-ethoxyearbonyl-4-methyl-6-oxo-l, V82 1.17 .12 I. 80 1.08 .11 1 3,3a,7-t etrazaindene, 3.0 g. I I I. I 2-amino-fi-carb0xy-4-methy1-6-oxo-l,3,3a,7 08 1. 11 '174 1.17 14 k I tetrazaindene, .75 g. I V I- g (k) 2- j 02-42-gnethyl-6-0xo-L3,3a,7-tetraza1n- 89 1.17 .12 100. 1.05 13 W ene,. g. I VI I II 1 I The photographic emulsions used in practicingmy invention are of the developingout type. v r The emulsions can be chemically sensitized byany of The emulsions can be digested V with naturally active gelatin, or sulfur compounds can V be addedsuch as those described in Sheppard U.S. Patent 1,574,944, issued March 2, 1926, Sheppard et a1. U.S.

Patent 1,623,499, issued April 5, 1927,'and Sh'eppard'et al. U.S. Patent 2,410,689, issued November 5, 1946.

The emulsions "can also be sensitized with salts of the noble metals such as ruthenium, rhodium, palladium,

iridium, land platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate,

l and sodium chloropalladite, which are used for ,sensitizing in amounts below that which produces any substantial panchromatic, iand infrarred' sensitive emulsions. They.

v may be added to. the emulsionibefore or after any sensitizing dyes which are used. ,Various silver salts may be, used asnthe sensitivesalt suchas silverbromide, silver iodide, silver chloride, or mixed silver halides, such as silver chlorobromide andsilver bromoiodide; The agents rnay be used in emulsions intended for color photography, for examplegemulsions containing color-forming. couplers or'emulsions to'be developed by 'solutions' containing couplers or othercolor-generating materials,

emulsions of the mixed-packet type, suchfas described in Godowsky U.S. Patent 2,698,794, issued January 4,1955; or emulsionsof the minedgrain type, such as described in Carrolland Hanson U.S. Patent 2,592,243, issued April gold salts as described in Waller et al. U.S. Patent; 2,399,083, issued April 23, 19 46, and Damschroder et al.

U.S. Patent 2,642,361 issued June 16, 1963. Suitable compounds are potassium'chloroaurite, potassium aurithiocyanate, potassium chloroauratc, auricf trichloride and 2-aurosultobenzothiazole. metho chloride. I I v "The emulsions can also, be che icallysensitized with reducingagents such as stannousv salts (Carroll U.S.

, Patent*2,487,i85 0, issued November 15 1949), polyam ine' s,

I such as diethylene tria'mine' (Lowe and Jones US. Patent 2,518,698, issued August 15., 1950);, polyamines, such as" spermine (Lowe and Allen U.S. Patent 2,5 2 1 ,925 issued SeptemberlZ, 19 50,),or,bis(,8raminoethyl)sulfide and its indifiusion transfer 'processes which utilizethe: undevel- 8, 1952. These agents can also be used in emulsions which forrn latent images predominantly'on the. surface of thesilver halideiicrystal or in emulsions which form latent'irnagespredominantly inside the silver halide crys- B en 2;2.59; d APr l. 1 52-f I Thesernay also be usedin emulsions intended for use -tal, such asithose described in Davey and Knott U.S.

oped silverihalide inthe nonimage areas of the negative.

' Such processes are described in Rott U.S. Patent 2,352,014,

.to form a positiyeby dissolving the undeveloped :silver halide and precipitating it on a receiving layer incl'os'e proximity ,tof the original silver halide emulsionlayer.

s ed 11 m; 2. 9 4 a d ld U-S- iefi 9. issuedJanuary 29, 1952'; 2,698,236; issued December 28,

1954, and 2,5 3,181, issued 'February 27; '1'95'1;-a' Yackel' et a1. Uisg'patent apPlicationjSe rial No. 586,705, filed May 23, 1956. They may also be used in color transfer processes which utilize the diffusion transfer of an imagewise distribution of developer, coupler or dye, from a light-sensitive layer to a second layer, While the two layers are in close proximity to one another. Color processes of this type are described in Land U.S. Patents 2,559,643, issued July 10, 1951, and 2,698,798, issued January 4, 1955; Land and Rogers Belgian Patents 554,933 and 554,934, granted August 12, 1957; International Polaroid Belgian Patents 554,212, granted July 16, 1957, and 554,935, granted August 12, 1957; Yutzy U.S. Patent 2,756,142, granted July 24, 1956, and Whitmore and Mader U.S. patent application Serial No. 734,141, filed May 9, 1958. They may also be used in emulsions intended for use in a monobath process such as described in Haist et al. U.S. Patent 2,875,048, issued February 24, 1959, and in web-type processes, such as the one described in Tregillus et al. US. patent application Serial No. 835,473, filed August 24, 1959.

in the preparation of the silver halide dispersions employed for preparing silver halide emulsions, there may be employed as the dispersing agent for the silver halide in its preparation, gelatin or some other collodial material such as colloidal albumin, a cellulose derivative or a synthetic resin, for instance, a polyvinyl compound. Some colloids which may be used are polyvinyl alcohol or a hydrolyzed polyvinyl acetate as described in Lowe U.S. Patent 2,285,215, issued June 16, 1942; a far hydrolyzed cellulose ester such as cellulose acetate hydrolyzed to an acetyl content of 19-26% as described in U.S. Patent 2,327,808 of Lowe and Clark, issued August 24, 1943; a water-soluble ethanolamine cellulose acetate as described in Yutzy U.S. Patent 2,322,085, issued June 15, 1943; :1 polyacrylamide or an imidized polyacrylamide as described in Lowe, Minsk and Kenyon U.S. Patent 2,541,474, issued February 13, 1951; zein as described in Lowe U.S. Patent 2,563,791, issued August 7, 1951; a vinyl alcohol polymer containing urethane carboxylic acid groups of the type described in Unruh and Smith US. Patent 2,768,- 154, issued October 23, 1956; or containing cyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetate copolymer as described in Unruh, Smith and Priest U.S. Patent 2,808,331, issued October 1, 1957; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in U.S. Patent 2,852,382, of Illings- Worth, Dann and Gates, issued September 16, 1958.

As indicated above, the tetrazaindene compounds of my invention are particularly useful in the production of X-ray materials, since they have little or no measurable effect upon the spectral sensitivity of photographic silver halide emulsions. This makes many of these tetrazaindene compounds especially adaptable for X-ray use, where the emulsions are generally double coated, that is, one emulsion being coated on each side of a transparent support. These emulsions are generally not spectrally sensitized.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What I claim as my invention and desire seccured by Letters Patent of the 'United States of America is:

1. A photographic silver halide emulsion containing a stabilizing amount of a compound selected from those represented by the following general formula:

3. A photographic silver halide emulsion containing a stabilizing amount of the compound represented by the following formula:

4. A photographic silver halide emulsion containing a stabilizing amount of the compound represented by the following formula:

H N f 5. A photographic silver halide emulsion containing a stabilizing amount of the compound represented by the following formula:

6. A photographic silver halide emulsion containing a stabilizing amount of the compound represented by the following formula:

7. A photographic element especially adaptable for use in X-ray photography comprising a transparent support and coated on each side of said transparent support a nonspeet-rally sensitized photographic silver halide emulsion containing a stabilizing amount of a compound selected from those represented by the following general formula:

are

wherein R represents a member selected from the class co'n'sistingbf arn'ino, rnethylamino, mercapto, methylmercap'to and ethylmercapto, R represents a member selected from the class consisting ofa hydrogen atom and a lower alkylgroup, R represents a member selected from the'class consisting of a hydrogen atom,'a carboxyl radical 'a'n'da carbalkoxylradical containing from 2 to 5 carbon "atoms. V

8. A photographic element especially adaptable for use in 'X-ray photography comprising a transparent sup port and coated on each side of said transparent support a nonspectrally sensitized photographic silver halide emulsion containing a stabilizing amount of a compound represented by the following formula:

9. A photographic element especially adaptable for use in X-ray photography comprising a transparent support'and coated on each side of said transparent support a nonspectrally sensitized photographic silver halide emulsion containing a stabilizing amount ,of a compound represented by the following formula:

N HOOO(E\ o (3H3 r 10. A photographic element especially adaptable for use in X-ray photography comprising a transparent support and coated on each side of said transparent support,

11. A photographic element especiallytadaptable for use in X-ray photography comprising a transparent sup:

' port and coated on each side of said transparent support a nonspectrally sensitized photographic silver halide" emulsion containing a stabilizing amount of a compound represented by the following formula:

a 'non spectrally sensitized photographic silver halide emulsion containing a'stabilizing amount of a compound represented by the following formula:

12. ,A photographic element especially adaptable for use in X-ray photography comprising a transparent support and coated on each side' of said transparent support a nonspcctrally V sensitized photographic silver halide emulsion containing a stabilizing amount of a compound represented by the following formula:

References Cited by the Examiner 'UNITED STATES PATENTS 2,526,477 10/50 Heirnbach 96109 2,5663658- 9/51 Fry 260256.4 2,735,769 2/56 Allen et a1. 96109 2,956,876 10/60 Spath 96-7-109 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,202,512 August 24, 1965 Leslie Alfred Williams It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification, between lines 8 and 9, insert the following:

Claims priority, application Great Britain Nov. 11, 1960, 38,919/60.

column 10, lines 33 to 39, the formula should appear as shown below instead of as in the patent:

Signed and sealed this 29th day of March 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A STABILIZING AMOUNT OF A COMPOUND SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FOROMULA: 